The present invention relates to a method for operating a navigation system, having a digital map base which includes a reproduction of actual geographic regions and data of geographic elements, as well as having a device, such as a control panel with a display device that calls up the data and processes them, the data being summarized in the digital map base in the form of geographically defined tiles, as generically defined by the preamble to claim 1.
In means of locomotion, such as motor vehicles, aircraft or ships, permanently installed navigation systems rapidly, simply and securely guide an operator of the means of locomotion toward a desired destination, without having to plan a route in advance at great effort and without having to obtain and study map material accordingly beforehand. To that end, navigation data are stored as a digital map base in the navigation system, for instance on CD-ROM, and based for instance on maps, regional maps or road maps. The navigation device for instance uses the GPS (Global Positioning System) in order to ascertain the location at that moment and calculate appropriate navigation directions that lead to a predetermined destination. The navigation data for instance contain data about streets and roads for motor vehicles as well as more extensive geographic information, such as mountains, lakes, forests, developed regions, or other topographical elements, or extensive information, such as restaurants, hotels, sights to see, or other information.
The digital map base is essentially a reproduction of the actual road network and the corresponding geographic environment. This information from the digital map base is displayed on a control panel on a display for the sake of informing the driver; for the sake of simplicity of illustration, the degree of detail or number of geographic characteristics displayed can be selected differently for different situations. For instance on an overview map, only limited access highways are shown, while a map of the inner city should include details down to the extent of residential buildings. This choice of the map details displayed has quite a substantial influence on the clarity and legibility of maps displayed on the basis of the digital map base; this is especially important for displays in vehicles, since a driver should be able at a glance to see all the necessary information to follow a given route. Logically, the map displays cannot all be produced by the same generally defined rules; relative weighting of the display elements must be done instead. For instance, an overview map of the Ruhr in Germany ought not to show all the autobahns. By comparison, a map on the same scale in Arizona could show even very minor roads.
In navigation systems for motor vehicles, it is appropriate for the navigation module, which makes the digital map base available, to be separated from the devices that display it, and these should also be developed separately from one another. A predefined interface is then necessary, for access to the digital map base of the navigation module. This interface must make it possible, in the display device, to produce digital maps with good clarity on different scales.
Such interfaces are known, produced for instance by the companies known as NAVTECH (http://www.navtech.com) or Etak Inc. (http://www.etak.com). These interfaces enable access to the physical memory format of the digital map base. In different vehicles, however, different digital map bases are used. Furthermore, on access by means of the navigation module, for instance for internal route calculation, and control panel computers, for instance for generating a display of a detail of the digital map base on the display device, access conflicts can occur. Also, the elements in the digital map bases are described xe2x80x9cdirectlyxe2x80x9d; that is, an autobahn is a road of the motorway or limited access highway class, with a number. It has been found that standardization and unification of the classification of map elements is possible only on a very unsatisfactory level that cannot be used to generate a display.
Furnishing the data for display on the display device on the control panel of a navigation system is often done in the form of geographically defined tiles. A tile network is formed by dividing up the surface of the Earth for the map into a network of tiles of the same geographical area, comparable to the grid squares on a conventional printed map. Each grid square is equivalent to one tile. The control panel calls up a tile and shows it on the display device. The information contained in the tile is also used for calculating a route. This has the advantage on the one hand of achieving simple definition of the data to be requested from the digital map base, because a tile is simply called up, and all the data contained in this tile regarding geographic elements are transmitted. In addition, decoupling between the screen portion and data maintenance is also achieved. On the other hand, it is a major disadvantage of tiles that data or information that may be of interest are located outside that particular tile or are unavailable at the edge of the tile, because they have been cut off by so-called xe2x80x9cclippingxe2x80x9d and were not also transmitted. Data on the edges of tiles may also require calculation for the sake of route calculation. Rounding errors then occur, if for instance a line originating at a starting point is rounded off by xe2x80x9crounding downxe2x80x9d to a coordinate located on the edge of the tile. In the neighboring tile, the coordinate located on the edge of the tile and calculated from the end point of the line can be rounded by xe2x80x9crounding upxe2x80x9d to some other coordinate. The tile coordinates of the line are then not located on one another at the edge of the tile. Hence this method for determining the tile edge coordinates (called clipping) is complicated and vulnerable to error.
It is the object of the present invention to make an improved method of the above type available which overcomes the aforementioned disadvantages and achieves a more-flexible display that is closer to reality.
This object is attained by a method of the type defined above having the characteristics defined by the body of claim 1.
To that end, the invention provides that when a tile is requested from the digital database, data of geographic elements which have an area beyond past the edge of the tile are transmitted in such a way that data pertaining to these geographic elements are also collected and transmitted outside the requested tile.
This has the advantage that on the one hand the device that calls up the data need not itself know the size of the tile, and a tile can merely be called up by indicating a pair of coordinates, and on the other hand, data pertaining to geographic elements that overlap the edge of the tile can also be present, adjacent to the edge of the tile, outside the tile. xe2x80x9cClippingxe2x80x9d at the boundaries of tiles is unnecessary. In addition, a xe2x80x9cmapxe2x80x9d, regardless of the size of the tile, can be assembled for display on the display device, so that tile boundaries need not necessarily be visible in the display. In addition, lapses in the map display that are otherwise caused by rounding errors in xe2x80x9cclippingxe2x80x9d algorithms at the tile boundaries are avoided.
Advantageous refinements of the method are described in dependent claims 2-5.
For instance, when a tile is requested, data of geographic elements which while located outside the requested tile are nevertheless adjacent to the edge of the requested tile within a predetermined region are additionally transmitted.
A tile request without knowledge of the internal coordinate format of the digital tile and without knowledge of the size of the tile is attained in that the request of a tile is parametrized via geographical coordinates.
If certain data elements, such as hotels, railroad lines, restaurants or the like, are known in the device that calls up and processes the data, then expediently a request of a tile is done by inclusion and/or exclusion of such data elements contained in the tile.
In a preferred embodiment, when a tile is requested from the digital database, data on the requested tile are additionally transmitted that include indications of the size of the tile, area of the tile, maximum area with adjacent and protruding geographic elements, data elements contained in the tile, and/or other information describing the tile. Because data elements contained in the tile are additionally transmitted, the device that requests and processes the data can optimize subsequent requests for data such that not all the data elements contained in the tile may optionally be transmitted, and instead individual groups of data elements, such as streets, roads, hotels, railroad lines, restaurants or the like are excluded when the tile is requested.